Call the 1K desk. You will not lose the UG on the international portion.
Polaris lounge @
sfo is worth the extra time.
I am on the same SFO-SIN flight as you tomorrow and on the 6.15am flight from SAN but I chose the earlier flight not for the Polaris lounge but because I do not want a flight delay into SFO to cause me to miss the flight.
I would ask for the 1K desk for the earlier DEN-SFO flight so you do not misconnect